1. Field of the Invention
The present invention relates to cartridges for ink jet print heads of the type wherein the ink reservoir is bounded by two thin films and a rigid frame. The invention provides novel cartridges made by a process wherein the frame is formed in a one-shot plastic injection molding step and the thin films are attached to the frame by adhesive bonding.
2. Prior Art
High capacity color ink jet printers configured around independent single color pens are currently commercially available. Typical pens or cartridges of the type suitable for use in such printers are shown in U.S. Pat. Nos. 5,280,300 and 5,325,119 and EP published applications 0 561 051 and 0 583 153.
As shown in FIG. 5 a typical prior art print head cartridge includes a frame 10 having a flexible ink-impervious thin membrane 12 and a side cover 14 disposed on one side. A second membrane and a second side cover (not shown) are disposed on the opposite side of frame 10. The frame 10 is formed by a two-shot plastic injection molding process. A rigid outer frame 16 (FIG. 6) of high melt temperature plastic is formed in a first mold during a first injection molding step. The rigid outer frame 16 is then placed in a second mold and a low melt temperature rubber-like plastic is injected into the mold. The rubber-like plastic forms an inner frame 18 molded onto outer frame 16, the inner and outer frames forming the frame 10 as shown in FIG. 7.
As shown in FIGS. 7 and 8, the inner frame 18 has oppositely facing flat side surfaces 20, 20' which extend around the entire periphery of the inner frame 18. The ink-impervious thin membranes 12 and 12' (FIG. 8) are heat staked to the surfaces 20 and 20' thereby forming a chamber or ink reservoir 22 bounded on opposite sides by the thin membranes and bounded around its periphery by the inner surface 24 of the inner frame 18.
The outer frame 16 is molded to have a downwardly extending nose portion 16A (FIG. 6) having therein a standpipe 26 as shown in FIG. 6. The standpipe 26 has an ink flow channel 28 which extends through the standpipe and outer frame 16 to the bottom surface 30 of the nose. The inner frame 18 is molded around the standpipe 26 so that the opening into channel 28 is not closed as the inner frame 18 is molded onto outer frame 16. This permits ink to flow from reservoir 22 through the channel 28 to the bottom surface of the nose from whence it may be ejected through a nozzle plate (not shown).
The prior art print head cartridges shown in FIGS. 5-8 has a disadvantage in that the frame requires two separate and distinct molding steps thus making the frame 10 almost twice as expensive to manufacture as a similar frame formed in a single molding step. The device cannot be formed in a single molding step because different materials are required for the inner frame 18 and outer frame 16. The requirement that the impervious films 12, 12' be heat staked to the inner frame 16 dictates that the material used in forming the inner frame be a low melt temperature, rubber-like material. That is, the material comprising the inner frame must have a melt temperature less than that of the membrane material to prevent tear or damage to the membrane during the staking process and so that it melts to form a bond with the membranes 12,12' during the heat staking of the membranes. Since the inner frame material is somewhat flexible, the rigid outer frame must be made of a stiff material in order to support the flexible ink reservoir.
As discussed in EP published application 0 561 051, print head cartridges made by the two-shot molding process have a further disadvantage in that the ink reservoir may leak where the inner frame 18 is molded around the standpipe 24.